RE: [xdp-hints] [PATCH bpf-next v7 5/5] igc: Add launch time support to XDP ZC
From: Song, Yoong Siang
Date: Tue Feb 04 2025 - 09:50:04 EST
On Tuesday, February 4, 2025 10:04 PM, Fijalkowski, Maciej <maciej.fijalkowski@xxxxxxxxx> wrote:
>On Tue, Feb 04, 2025 at 02:14:00PM +0100, Song, Yoong Siang wrote:
>> On Tuesday, February 4, 2025 6:10 PM, Fijalkowski, Maciej<maciej.fijalkowski@xxxxxxxxx> wrote:
>> >On Tue, Feb 04, 2025 at 08:49:07AM +0800, Song Yoong Siang wrote:
>> >
>> >> Enable Launch Time Control (LTC) support for XDP zero copy via XDP Tx
>> >> metadata framework.
>> >>
>> >> This patch has been tested with tools/testing/selftests/bpf/xdp_hw_metadata
>> >> on Intel I225-LM Ethernet controller. Below are the test steps and result.
>> >>
>> >> Test 1: Send a single packet with the launch time set to 1 s in the future.
>> >>
>> >> Test steps:
>> >> 1. On the DUT, start the xdp_hw_metadata selftest application:
>> >> $ sudo ./xdp_hw_metadata enp2s0 -l 1000000000 -L 1
>> >>
>> >> 2. On the Link Partner, send a UDP packet with VLAN priority 1 to port 9091
>> >> of the DUT.
>> >>
>> >> Result:
>> >> When the launch time is set to 1 s in the future, the delta between the
>> >> launch time and the transmit hardware timestamp is 0.016 us, as shown in
>> >> printout of the xdp_hw_metadata application below.
>> >> 0x562ff5dc8880: rx_desc[4]->addr=84110 addr=84110 comp_addr=84110 EoP
>> >> rx_hash: 0xE343384 with RSS type:0x1
>> >> HW RX-time: 1734578015467548904 (sec:1734578015.4675)
>> >> delta to User RX-time sec:0.0002 (183.103 usec)
>> >> XDP RX-time: 1734578015467651698 (sec:1734578015.4677)
>> >> delta to User RX-time sec:0.0001 (80.309 usec)
>> >> No rx_vlan_tci or rx_vlan_proto, err=-95
>> >> 0x562ff5dc8880: ping-pong with csum=561c (want c7dd)
>> >> csum_start=34 csum_offset=6
>> >> HW RX-time: 1734578015467548904 (sec:1734578015.4675)
>> >> delta to HW Launch-time sec:1.0000 (1000000.000 usec)
>> >> 0x562ff5dc8880: complete tx idx=4 addr=4018
>> >> HW Launch-time: 1734578016467548904 (sec:1734578016.4675)
>> >> delta to HW TX-complete-time sec:0.0000 (0.016 usec)
>> >> HW TX-complete-time: 1734578016467548920 (sec:1734578016.4675)
>> >> delta to User TX-complete-time sec:0.0000
>> >> (32.546 usec)
>> >> XDP RX-time: 1734578015467651698 (sec:1734578015.4677)
>> >> delta to User TX-complete-time sec:0.9999
>> >> (999929.768 usec)
>> >> HW RX-time: 1734578015467548904 (sec:1734578015.4675)
>> >> delta to HW TX-complete-time sec:1.0000 (1000000.016 usec)
>> >> 0x562ff5dc8880: complete rx idx=132 addr=84110
>> >>
>> >> Test 2: Send 1000 packets with a 10 ms interval and the launch time set to
>> >> 500 us in the future.
>> >>
>> >> Test steps:
>> >> 1. On the DUT, start the xdp_hw_metadata selftest application:
>> >> $ sudo chrt -f 99 ./xdp_hw_metadata enp2s0 -l 500000 -L 1 > \
>> >> /dev/shm/result.log
>> >>
>> >> 2. On the Link Partner, send 1000 UDP packets with a 10 ms interval and
>> >> VLAN priority 1 to port 9091 of the DUT.
>> >>
>> >> Result:
>> >> When the launch time is set to 500 us in the future, the average delta
>> >> between the launch time and the transmit hardware timestamp is 0.016 us,
>> >> as shown in the analysis of /dev/shm/result.log below. The XDP launch time
>> >> works correctly in sending 1000 packets continuously.
>> >> Min delta: 0.005 us
>> >> Avr delta: 0.016 us
>> >> Max delta: 0.031 us
>> >> Total packets forwarded: 1000
>> >>
>> >> Signed-off-by: Song Yoong Siang <yoong.siang.song@xxxxxxxxx>
>> >> ---
>> >> drivers/net/ethernet/intel/igc/igc_main.c | 42 +++++++++++++++++++++--
>> >> 1 file changed, 40 insertions(+), 2 deletions(-)
>> >>
>> >> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c
>> >b/drivers/net/ethernet/intel/igc/igc_main.c
>> >> index c3edd8bcf633..535d340c71c9 100644
>> >> --- a/drivers/net/ethernet/intel/igc/igc_main.c
>> >> +++ b/drivers/net/ethernet/intel/igc/igc_main.c
>> >> @@ -2951,9 +2951,33 @@ static u64 igc_xsk_fill_timestamp(void *_priv)
>> >> return *(u64 *)_priv;
>> >> }
>> >>
>> >> +static void igc_xsk_request_launch_time(u64 launch_time, void *_priv)
>> >> +{
>> >> + struct igc_metadata_request *meta_req = _priv;
>> >> + struct igc_ring *tx_ring = meta_req->tx_ring;
>> >> + __le32 launch_time_offset;
>> >> + bool insert_empty = false;
>> >> + bool first_flag = false;
>> >> +
>> >> + if (!tx_ring->launchtime_enable)
>> >> + return;
>> >> +
>> >> + launch_time_offset = igc_tx_launchtime(tx_ring,
>> >> + ns_to_ktime(launch_time),
>> >> + &first_flag, &insert_empty);
>> >> + if (insert_empty) {
>> >> + igc_insert_empty_packet(tx_ring);
>> >> + meta_req->tx_buffer =
>> >> + &tx_ring->tx_buffer_info[tx_ring->next_to_use];
>> >
>> >in this case I think you currently are leaking the skbs and dma mappings
>> >that igc_init_empty_frame() did. you're going to mix
>> >IGC_TX_BUFFER_TYPE_XSK with IGC_TX_BUFFER_TYPE_SKB and the latter is not
>> >explicitly initialized. Even though IGC_TX_BUFFER_TYPE_SKB happens to be
>> >equal to 0, igc_tx_buffer::type is never cleared in the tx clean desc
>> >routine.
>> >
>>
>> Hi Fijalkowski Maciej,
>>
>> Thanks for your inputs.
>>
>> Yes, you are right, IGC_TX_BUFFER_TYPE_SKB is mixed together with
>> IGC_TX_BUFFER_TYPE_XSK. Regarding the skb and dma map,
>> following code in igc_clean_tx_irq() will free the skb and unmap the dma,
>> Do these answer your concern on leaking?
>>
>> igc_main.c:3133: case IGC_TX_BUFFER_TYPE_SKB:
>> igc_main.c-3134- napi_consume_skb(tx_buffer->skb, napi_budget);
>> igc_main.c-3135- igc_unmap_tx_buffer(tx_ring->dev, tx_buffer);
>> igc_main.c-3136- break;
>>
>> Regarding the igc_tx_buffer::type never cleared, I think the
>> important thing is making the igc_tx_buffer::next_to_watch NULL
>> to indicate no remaining packet. Since transmit function will
>> always set the igc_tx_buffer::type to a proper type,
>
>igc_init_tx_empty_descriptor() does not set ::type, that was my point. So
>these empty descs might be treated as IGC_TX_BUFFER_TYPE_XSK, which is
>wrong and your qouted code above will never get called. You will then leak
>skb and dma map plus you will confuse XSK code due to xsk_frames miscount.
>
Now I understand what you mean. Thanks for the explanation. I will add the
missing IGC_TX_BUFFER_TYPE_SKB initialization in igc_init_empty_frame(),
as below.
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -1096,6 +1096,7 @@ static int igc_init_empty_frame(struct igc_ring *ring,
return -ENOMEM;
}
+ buffer->type = IGC_TX_BUFFER_TYPE_SKB;
buffer->skb = skb;
buffer->protocol = 0;
buffer->bytecount = skb->len;
With above, IMHO, we no need to clear igc_tx_buffer::type,
Are you agree?
>> I think it is optional for us to clear it.
>> Is that make sense to you?
>>
>> >> + }
>> >> +
>> >> + igc_tx_ctxtdesc(tx_ring, launch_time_offset, first_flag, 0, 0, 0);
>> >> +}
>> >> +
>> >> const struct xsk_tx_metadata_ops igc_xsk_tx_metadata_ops = {
>> >> .tmo_request_timestamp = igc_xsk_request_timestamp,
>> >> .tmo_fill_timestamp = igc_xsk_fill_timestamp,
>> >> + .tmo_request_launch_time = igc_xsk_request_launch_time,
>> >> };
>> >>
>> >> static void igc_xdp_xmit_zc(struct igc_ring *ring)
>> >> @@ -2976,7 +3000,13 @@ static void igc_xdp_xmit_zc(struct igc_ring *ring)
>> >> ntu = ring->next_to_use;
>> >> budget = igc_desc_unused(ring);
>> >>
>> >> - while (xsk_tx_peek_desc(pool, &xdp_desc) && budget--) {
>> >> + /* Packets with launch time require one data descriptor and one context
>> >> + * descriptor. When the launch time falls into the next Qbv cycle, we
>> >> + * may need to insert an empty packet, which requires two more
>> >> + * descriptors. Therefore, to be safe, we always ensure we have at least
>> >> + * 4 descriptors available.
>> >> + */
>> >> + while (xsk_tx_peek_desc(pool, &xdp_desc) && budget >= 4) {
>> >> struct igc_metadata_request meta_req;
>> >> struct xsk_tx_metadata *meta = NULL;
>> >> struct igc_tx_buffer *bi;
>> >> @@ -3000,6 +3030,12 @@ static void igc_xdp_xmit_zc(struct igc_ring *ring)
>> >> xsk_tx_metadata_request(meta, &igc_xsk_tx_metadata_ops,
>> >> &meta_req);
>> >>
>> >> + /* xsk_tx_metadata_request() may have updated next_to_use */
>> >> + ntu = ring->next_to_use;
>> >> +
>> >> + /* xsk_tx_metadata_request() may have updated Tx buffer info */
>> >> + bi = meta_req.tx_buffer;
>> >> +
>> >> tx_desc = IGC_TX_DESC(ring, ntu);
>> >> tx_desc->read.cmd_type_len = cpu_to_le32(meta_req.cmd_type);
>> >> tx_desc->read.olinfo_status = cpu_to_le32(olinfo_status);
>> >> @@ -3017,9 +3053,11 @@ static void igc_xdp_xmit_zc(struct igc_ring *ring)
>> >> ntu++;
>> >> if (ntu == ring->count)
>> >> ntu = 0;
>> >> +
>> >> + ring->next_to_use = ntu;
>> >> + budget = igc_desc_unused(ring);
>> >
>> >why count the remaining space in loop? couldn't you decrement it
>> >accordingly to the count of descriptors you have produced? writing ntu
>> >back and forth between local var and ring struct performance-wise does not
>> >look fine.
>> >
>>
>> Yes, I can check the number of used descriptor in xsk_tx_metadata_request()
>> by introducing a new field named used_desc in struct igc_metadata_request,
>> and then decreases the budget with it.
>>
>> Do this way looked good to you?
>
>Yes this makes sense to me, thanks!
>
Thanks, I will rework and submit next version.
>>
>> Thanks & Regards
>> Siang
>>
>> >> }
>> >>
>> >> - ring->next_to_use = ntu;
>> >> if (tx_desc) {
>> >> igc_flush_tx_descriptors(ring);
>> >> xsk_tx_release(pool);
>> >> --
>> >> 2.34.1
>> >>
Thanks & Regards
Siang